Small-scale turbine is 'very efficient' at lower wind speeds

The creators of a vertical-axis wind turbine say their new design could at least double the energy it captures at lower speeds.

Pembrokeshire-based Quiet Revolution has found a way to make small changes to the size, aerodynamics and electrical conversion and control systems of its small-scale turbines that yield substantial increases in the amount of energy produced.

Initial tests suggest the new design is particularly effective at lower wind speeds, meaning it could open up locations that were not previously cost effective as turbine sites.

‘The challenge in general for small wind is that there is a vast range of power outputs that we need to deal with but also the rate at which it changes,’ Richard Cochrane, chief technical officer at Quiet Revolution, told The Engineer.

‘The vertical axis gives us an inherent advantage in turbulent wind conditions as we don’t need to turn to face the wind. But direction is just one aspect of it. It’s also about maintaining your efficiency in rapidly changing wind velocities.

‘You need a broad, well-rounded aerodynamic design combined with an active control system that can speed up and follow those gusts to capture that energy very efficiently.’

He added: ‘We’ve also done a number of things within the structure to simplify the mechanical design to make it much quicker and easier to manufacture and therefore cheaper as well.’

The company collected data from a number of its QR5 wind turbines already in the field, as well as from lab testing, in order to make the adjustments.

Further tests are needed to confirm the exact increase in power output. ‘The relative improvement is not so good on a high-wind-speed site where the current generator was more optimal anyway,’ said Cochrane.

Readers' comments
(3)

Graham Field | 1 Jul 2011 7:50 pm

Vertical axis is the way forward. Unlike the current horizontal axis turbines, where interaction between the rotating blades and the mask generate appreciable and annoying 'whomp' noises as the blade passes the mast, the vertical blades whirl around in near silence. Given the simpler construction requirements, lower weight, and smaller groundworks, if feel we should be giving them much greater attention. It would be great to scale one up! (I'm betting they would be a lot less visually intrusive too.)

Probably an inflatable tower would go a long way toward flexible operation, to generate a pun. For maintenance and installation, you could utilize a much, much stronger tower, with no guywires, with a structure based on decreasing-diameter inflatable donuts. And in extreme weather, one person can bring it to ground for zero damage.

I'll believe it when I see it. Even the most efficient vertical axis turbines - Darrieus rotors - suffer from intrinsic inefficiencies compared with horizontal axis machines. If their blades are curved into the central axis at the ends, there must be two hubs - not one. If the blades are straight they need to be spaced away from the axis by horizontal spokes: extra weight. The swept disks of horizontal axis machines always face the wind, so all their blades are active throughout each rotation. As the blades of a vertical axis machine rotate, the relative angle & speed of the oncoming air change greatly at each point along each blade. This can be partly overcome by very sophisticated blade twisting & angle-of-attack control technology - but then the controlling device must be installed in at least two hubs - top & bottom - which must work in perfect synchrony. Just one simple blade angle controller is fine for a horizontal axis machine. Stressing of the blades of a vertical axis machine is also complex, & is at odds with the best aerofoil profile required along the blades. The blade stress distribution in horizontal axis machines agrees well with the optimal tapered aerofoil shape. Vertical axis machines are subject to significantly greater fatigue-inducing changes in blade stress due to the rotating design, & are prone to uneven wear in the bearings because of prevailing wind directions. Some of these deficits may be negligible in a very small machine, but I doubt that a properly designed vertical axis turbine will ever outperform a properly designed horizontal axis turbine of the same price.